PPM technology rests on a simple but effective engineering device: the flywheel. The rotating flywheel is a store of kinetic energy that is used to power the vehicle. A typical PPM flywheel is made from steel laminates, 1m in diameter and 500kg mass, rotating at a maximum speed of 2,500rpm – simple, reliable and easily maintainable.
The flywheel allows the direct capture of brake energy (when slowing down or descending gradients) and its re-use for acceleration. Since the short-term power demand for acceleration is provided by the energy stored in the flywheel, there is no need a large engine or heavy-duty electrical supply along the whole length of the route.
The PPM concept allows maximum variability in the way the flywheel is ‘charged’:
- For zero emission operation with closely-spaced stops, the flywheel can be charged (in approx. 30 seconds) from an intermittent electrical supply at the stations only. The flywheel stores sufficient energy for the vehicle to reach the next stop in normal operation, and a battery is also provided for emergency use.
- For low-emission, high fuel efficiency and quiet self-powered operation, an on board LPG-fuelled automotive engine is used. A Compressed Natural Gas version is an alternative.
- Alternative possibilities include diesel- or hydrogen-fuelled internal combustion engines, or hydrogen fuel cells, while the intermittent electric version can be powered from solar cells or other renewable sources of electricity.
PPM Technology Allows:
- A 2.4-litre engine to transport sixty passengers.
- Zero-emission street tramways without any electrification.
- Variable vehicle size, boarding height, power source, appearance, interior layout…
- The best environmental performance of any comparable mode of transport..
Calculations show that the PPM 60/Class 139 vehicles operating on the Stourbridge branch line emit less than a fifth of the carbon dioxide produced per day by the conventional trains which previously worked on this route. This saving is achieved despite the fact that the PPM vehicles provide a 50% more frequent service.
It is now genuinely possible to reduce the cost of running a short-line rail service by half. The R&D achievement which has made it possible began with an unusual experimental locomotive which worked at a colliery in North East England in the 1950s using energy stored in a spinning flywheel. Years of engineering development on flywheel energy led to the patenting of a flywheel-hydrostatic-hybrid driveline used to propel two small 60 passenger railcars on a train service at Stourbridge in the West Midlands. This has been a great technical success having operated for seven years as Britain’s most economical train service.
A BETTER WAY OF MOVING PEOPLE
Envisage a modern land-locked country which has most things that are needed; houses, schools, shops, clinics, parks but the one thing missing is a means of moving about other than exclusively on foot. In such circumstances most distances travelled would be short, people would live in villages not cities and so, for wealth and knowledge to expand, intelligent thinking would in due course be applied to creating a means of transport quicker and less tiring than on foot. Then someone invents the wheel! A committee of the great and good puts their minds to reviewing the new opportunity to apply the wheel in order to deal with their most frequently undertaken journeys, of 1-10 miles. They come up with an 8-point specification for a mode of travelling which would take advantage of the newly-discovered wheels. So that the design would be optimised it was decided that the mover of people must be:-
- Safe to ride on.
- Predictable in direction so people on foot know where it is going.
- Separate from pathways where possible so as to avoid being delayed by people in the way.
- Quiet, so as not to disturb the peace.
- Running very frequently so that nobody would have to wait long.
- Easy to control, so drivers can be quickly trained.
- Able to carry baggage as well as passengers.
- Carrying a good number of people in order to spread the cost.
In the 19th Century, at a time when most people walked, the true beginning of public transport on land occurred when something became cheap enough for ordinary people to ride, the vehicle concerned took the form of the tram. Playing a central role in the Judy Garland film ‘Meet Me in St Louis’, set at the beginning of the previous century, the trolleys and streetcars became ideal people movers for short urban journeys
One of the mysteries of the 20th Century is why trams, as they were called in Britain, suddenly went out of fashion. In a short period of years up to 1960 over 200 towns and cities scrapped their clean, reliable and fairly quick rail-based public transport systems, some of which had given good (and popular) service to ordinary people for over 50 years. It was assumed that with more people owning cars, and modern buses becoming available, it was the modern thing to do to dig up the rails because all local journeys would be made on roads.
Just as 100 years ago, taking a short journey on a ‘trolley’ was taken for granted, the millions of people making short transfers at facilities like airports use similar small vehicles called ‘APMs’ (automated people movers). In developing the initial concept of the People Mover in the 1990s, Parry Associates were seeking to revive the concept of the small, simple, frequently running rail based tram-type vehicle but in a modern form, like the APMs, not automated but with a driver.
After designing, constructing and trialling a series of 12 prototypes culminating in two temporary experimental services, Bristol Harbourside 1998-2000 and a one year Sunday only operation at Stourbridge in 2006, the Parry People Mover was finally specified for a permanent public service operation. The design specified was for a class of vehicle which can carry 60 people, the ‘PPM60’ or ‘Class 139’ in its railway classification.
The outcome is illustrated in the following two pages; Costs for operating the branch line halved- saving over £1 million for the public purse, energy use reduced to a third, passenger numbers doubled since taking over from the heavy rail based service and reliability matching the best performance of any other train service in Britain.
By June 2017 about 4 million passenger journeys have been taken on the Parry People Movers Class 139 railcars at Stourbridge, and it is recognised by the authorities as most promising as a means to cut costs on low risk, low speed branch lines and for opening new services on previously closed passenger railway lines.